By: Lesley Ke
The power of sonar systems, the noise that they produce, and the distance they can travel can undoubtedly have a negative effect on marine life.
A spokesperson for the UK’s Ministry of Defense (MoD) said in a statement: “Active sonar releases energy into the ocean, and there is evidence to suggest that this may have an effect on marine mammals. However, the precise scientific effects are not clear, thus the MoD has adopted a precautionary approach to mitigate effects on the marine environment. Environmental Impact Assessments are mandatory prior to the use of military sonar, and the ability to predict and detect marine life continues to be developed in order to minimize any perceived threats to marine life.”
Marine animals may experience damage to ears, damage to body tissue, and masking of communication. Whales that are fatally impacted can sink to the bottom of the ocean; therefore, the true death toll cannot be estimated. There are widespread concerns about the danger of high-intensity sonar to marine mammals, marine ecosystems, and the health of our depleted oceans. Fortunately, there soon may be an alternative to using sonars. Instead of sonars, we could detect submarines by paying more attention to natural sound.
"At the moment we treat all this natural sound as background noise, or interference, which we try to remove," says Lori Adornato, a project manager at US military research agency Darpa. "Why don't we take advantage of these sounds, see if we can find a signal?"
A grouper, a type of fish, can produce loud calls to scare off intruders. Their boom is a loud and low-frequency boom. They are territorial and will boom at any intruder. A booming grouper can be detected from 800m (2,640ft) away. However, not every single boom they produce means that they have met an intruder.
"We are trying to detect the echoes that are created when shrimp snaps reflect off of the vehicles," says Raytheon scientist Alison Laferriere. "In much the same way that a traditional sonar system detects echoes from the sound that its source generates."
Snapping shrimp, also known as the pistol shrimp, are called the loudest creatures on earth. They snap their claws so fast that they can create a temporary vacuum bubble in the water, called a cavitation bubble. That bubble then collapses, which releases a lot of energy that is powerful enough to stun prey. The snap of its claw releases a sound that can reach 218 decibels, which is louder than a gunshot.
"One of the biggest challenges we've faced is dealing with the huge amount of noise created by the shrimp themselves and the reflections of all of those sounds off of the surrounding area," says Laferriere.
Although a shrimps’ snap is quieter than traditional sonar, there can be thousands of shrimp snapping at the same time. The snapping shrimp sometimes live in colonies that can number over 300 members, and shrimp colonies are never quiet.
Even if we hear the reflections, the location of the sound source is still unknown. Laferriere's team has developed smart algorithms to analyze the sound and pick out a single snap. Then, they calculate the location of the shrimp, work out the path taken by the reflected sound and finally conclude where it was reflected.
Some of the echoes may have come off of stationary background objects, for example, fish, submarines, or unmanned underwater vehicles. So, Laferrier had to create computer models to determine which echoes could be ignored.
Hopefully, we don’t have to use sonars anymore, so we don’t harm marine animals, like whales. Instead, we can take advantage of natural sounds in the world.
Sources:
https://www.nature.com/articles/news.2008.997